| Background and objectivesThe ultraviolet ray in sunlight radiating to the Earth surface includes ultraviolet A (UVA) and ultraviolet B (UVB), accounting for the95～98%and the rest2～5%of the total ultraviolet intensity, respectively; While ultraviolet C (UVC) in sunlight is almost filtered out by the ozone layer. Ultraviolet ray may promote the synthesis of cutaneous vitamin D, and inhibit or kill bacteria living on the skin surface. In addition, the ultraviolet ray may also cure some skin diseases. However, too much ultraviolet radiation has the potential increasing the incidence of photosensitivity diseases. Although the biological effect of UVB is about1000times of that of UVA, its ability to penetrate into skin is weaker. UVB mainly injures the epidermis and the superficial dermis, leading to an acute reaction manifested as erythema and edema, or a chronic reaction including photo aging, immunosuppression and skin cancer. UVA may affect melanin synthesis in the epidermis, resulting in skin tanning; And it also has an impact on collagen and elastic fibers, and vessels in the dermis, which is associated with photo aging. Moreover, UVA and UVB may have a synergistic action in reducing cutaneous immune response and in increasing the incidence of skin cancer. Therefore, the aims of this study are to observe and analyze the changing pattern of ultraviolet intensities in the second half of summer in Zhengzhou, and to evaluate the role of an ultraviolet-proof umbrella in shielding against ultraviolet ray, in order to provide the scientific basis for residents in Zhengzhou to utilize sunlight rationally and to avoid sunlight damage in summer.MethodsUltraviolet A (UVA) and Ultraviolet B (UVB) intensities were measured seven times a day at two hours’interval in daytime from July16to August31,2011in Zhengzhou, both under sunlight and under an ultraviolet-proof umbrella. The data obtained in the two conditions were compared statistically with repeated measures analysis of variance.Results1. From July16to August31,2011, under sunlight, the mean intensities of UVA right over the ground at6:00,8:00,10:00,12:00,14:00,16:00and18:00were51.09±39.24μw/cm2,669.72±253.69μw/cm2,1553.06±669.31μw/cm2,2116.20±1007.22,1883.79±904.29μw/cm2,1000.69±480.39μw/cm2and276.22±124.89μw/cm2, respectively; and the intensities of UVB at the same time points were1.03±1.47μw/cm2,47.31±17.46μw/cm2,128.51±49.87μw/cm2,180.74±75.55μw/cm2,154.85±67.73μw/cm2,77.83±34.32μw/cm2and14.59±7.34μw/cm2, respectively.2. From July16to August31,2011, under an ultraviolet-proof umbrella the mean intensities of UVA right over the ground at6:00,8:00,10:00,12:00,14:00,16:00and18:00were0.06±0.35μw/cm2,2.44±1.22μw/cm2,5.83±2.57μw/cm2,7.94±3.31μw/cm2,7.24±3.35μw/cm2,4.26±2.27μw/cm2,0.88±0.66μw/cm2, respectively; and the intensities of UVB at the same time points were0μw/cm2,0μw/cm2,0μw/cm2,0.03±0.17μw/cm2,0.09±0.29μw/cm2,0μw/cm2,0μw/cm2, respectively.3. Both UVA and UVB intensities under the ultraviolet-proof umbrella were statistically significantly weaker than those under sunlight, all Ps<0.05. At the same time points except18:00, both under sunlight and under the ultraviolet-proof umbrella, the intensities of ultraviolet ray right above is different statistically significantly from the intensities in the east, west, south, north, all Ps<0.05.Conclusions1. From July16to August31,2011, both of the intensities of UVA and UVB elevate gradually from morning and reach their peaks at noon before going down; and they only change mildly in the morning and evening, while they fluctuate greatly around noon.2. UV-proof umbrella may shield against ultraviolet radiation effectively. |
